MultiORF

MultiORF is a term used to describe sequences that contain more than one open reading frame (ORF) that can be translated into distinct peptides or proteins. These ORFs may be arranged in different ways: overlapping ORFs occupying the same nucleotide region in different reading frames; alternative ORFs initiated at alternative start codons within the same transcript; and upstream ORFs located in the 5' leader region that can regulate translation of the main coding sequence.

In genomes, multiORF architecture contributes to proteome diversity and gene regulation. It is common in viral genomes where compact coding capacity benefits from overlapping frames, and in eukaryotes where uORFs can modulate translation efficiency. In bacteria and archaea, operons and small overlapping genes can also produce multiORF arrangements. The presence of multiple translated ORFs within a locus can influence expression levels, protein function, and evolutionary dynamics.

Detection and annotation of multiORFs rely on a combination of evidence. Computational gene prediction methods, ribosome profiling (Ribo-Seq), transcriptomics, and proteomics are used to identify and validate translated ORFs. Challenges include distinguishing functional ORFs from random short ORFs, dealing with short or non-canonical initiation sites, and interpreting overlapping coding sequences without misannotation.

Applications of multiORF knowledge include improving genome annotations, understanding translational regulation, and informing synthetic biology designs that encode multiple proteins from compact loci. See also: open reading frame, uORF, overlapping gene, ribosome profiling.